Evolution of resistance to combination insecticide products in the bed bug

Infestations of bed bugs, Cimex lectularius, are often difficult to control. In large part this is due to insecticide resistance. Currently, combination products that include a pyrethroid and a neonicotinoid insecticide are among the most effective means of controlling bed bugs.  However, previous research into the evolution of insecticide resistance to these combination products found that resistance to Temprid^® was rapid and that cross resistance to Transport^® occurred in two laboratory populations.  For this study, we determined a discriminating exposure time to explore changes in resistance over generations. With no ongoing selection, resistance levels to combination products did not decline over three generations in these laboratory populations. Next, we used log-dose probit analysis to evaluate results obtained from topical bioassays using the active ingredients of Temprid (imidicloprid and beta-cyflutrhin, the neonicotinoid and pyrethroid, respectively).  Results from this study showed that bugs initially selected with Temprid were less susceptible to the pyrethroid, but not the neonicotinoid (relative to control strains). This finding implies that our starting populations had more heritable variation for pyrethroid resistance than for neonicotinoid resistance.  The implications of this study for bed bug control and resistance management will be discussed.